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Q & A: Why is the universe expanding faster?

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Most recent answer: 02/03/2013
Q:
Why is the universe's expansion speeding up?
- Mark (age 19)
Chicago, Il, USA
A:
I wish I knew!  A Nobel Prize awaits the person who figures it out.  The current experimental facts are that it seems to be true.  There is a certain term in Einstein's equations that accommodates this accelerated expansion but at the present time there is no consensus about where it comes from. Another common term for this phenomenon is called 'Dark Energy'.   People are frantically designing astronomical experiments to look for effects of it. 
See:  for an example.

LeeH

(published on 11/07/2009)

Follow-Up #1: basic cosmology

Q:
This question is related to the expansion of the universe but I'll need to ask a few questions along with it. 1) Just after the big bang all energy rushed away from a single point and at the furthest part/edge of the universe we very very slight differencies in the cosmic microwave background. If I drew a line from the centre of the universe (or any other point) to the outside edge of the universe what would the distribution of energy/mass look like along the line (or if it is easier the plane). 2) Does energy affect/have gravity like mass? If not, then the first energy that started to condense as matter would have gravity and would slow to less than the speed of light and the rest of the energy would continue on. Could there be more mass nearer the center of the universe than at the edge? 3) Does gravity slow time down? If more matter condensed out near the center of the universe would time then move slower in the centre than at the edge. If this was the case (the centre of the universe being on average more dense then the edge) would it look to an observer near the centre of the universe then, that time moved faster at the edge and hence objects travelling away from the centre would look like they were travelling faster the further away they are giving the illusion that the universe's expansion was speeding up? p.s. I do apologise if this hasn't made sense, please let me know and I can try to reword my questions. This has honestly kept me up at night thinking about it.
- Tony (age 25)
Scotland
A:
These questions do indeed make sense, but they assume things about the universe that happen to be at odds with our best current knowledge of it.


1. There wasn't any special center point. Starting with any point, everything else moved away. There is no edge. Either the pattern goes on forever or it wraps around. On the large scale, the density at some particular age of the universe (in local standard time) is uniform

2. All forms of energy, including ones that we call mass, have the same effect on gravity.

3. There is no edge and no special center.

Mike W.





(published on 02/03/2013)

Follow-up on this answer.